Wet Blasting for Line Marking Removal

I. Introduction:

Line markings on roads and parking areas play a crucial role in reducing road accidents, controlling traffic, and highlighting obstructions. In addition, line marking is also used indoors, inside warehouses, car parks, factories, and public spaces. Over a period of time, due to vehicular traffic and the impact of the natural weather elements, the line marking paint starts to fade, peel away, or is discolored and is less visible. The line markings need to be stripped and reapplied   from time to time for safety and directional guidance. In addition, when roads are altered or additional lanes added, the existing line marking needs to be removed and fresh lines painted. Removing the line marking can be challenging due to the rough nature of the surface (bitumen, concrete, asphalt, etc.) as the objective is to remove it without damaging the underlying surface and without leaving a scar or ghost mark behind.

This article will provide you with an overview of the various processes in practice that are used to remove line marking paint and the machinery required in the process. This includes a short summary of different types of paint used in line marking and the different methods of line marking removal. In particular, the article provides a small brief on wet abrasive sand blasting equipment, and why in many circumstances wet sand blasting can be the ideal method of line marking removal.

II. The materials used for line marking

Line marking has evolved over the years to increase durability and enhance safety. The various types of paints that are commonly used in line marking are:

  • Quick-drying water-based paint: This contains pigments, resin, and water (solvent). Fine-grit glass beads may be added to the paint to serve as reflectors when light falls on it.
  • Thermoplastic paint:  This is a homogenous mix of binder resins and plasticizers. This mix of thermoplastic paint is heated up to 200° C and then fed to the line marking equipment. Fine grit glass beads may be added manually to the line marking before it dries (to serve as reflectors).
  • Cold plastic paints: Cold plastic paint consists of two or more chemical components, which, upon mixing will react to create the road marking.
  • Epoxy: This contains two parts, a pigmented resin base, and a catalyst. These two parts are mixed in a line marking truck, and heated to spraying temperature, before feeding it into the line sprayer.
  • Pre-formed polymer tapes that are affixed to the surface

III. Different methods used for Line Marking Removal

There are a few different processes used to remove line marking paint.

Grinding:  Grinding is a traditional method for removing the line marking and it is done by mechanically using one or more rotating abrasive wheels. This process is effective on all types of line marking paint,  but  it creates a lot of dust and reduces the surface thickness of the substrate. The grinding process also leaves ghost marks or scars visible on the surface. Such marks are not safe since they can confuse motorists and cause accidents. The ghost marks or scars may need a secondary process like water blasting to remove them.

Scarifying: A scarifier has tungsten tips mounted on the periphery of a rotating shaft (looks like a sprocket) and the tungsten tips remove the line marking. A scarifier is normally used for leveling concrete. It works aggressively, creates dust, leaves scratch marks, and may damage the underlying surface and remove a layer of the substrate.

Poly-planer: A poly-planer is nothing but a scarifier mounted on the front of a poly-planer truck. The truck operator has control to operate the scarifier and move the truck slowly to remove the line marking. Poly-planers have a self-levelling turntable to enable accurate cutting depths on uneven surfaces and offer a high production rate (quick removal). A poly-planer has a vacuum to suck the dust created by the scarifier, but this method is also aggressive, leaves scratch marks, and damage the underlying surface/remove a layer of the road.

High pressure water cleaning: This technique uses pressure water to remove paint markings from concrete and asphalt. Water blasting causes minimal scarring but is not powerful enough for the smoothening of uneven surfaces or for inlay and grooving applications and is not suitable for removal of thermoplastic paint. In addition, the use of high pressure water jet (30000 PSI or more) may not be suitable for old and porous asphalt roads. This process also uses an enormous amount of water.

Stripe hog water spraying machines for line removal: Stripe hog is high-pressure (40000 PSI) water blasting, and uses spray bar units with multiple jets. This is an efficient method for line removal and does not leave scars or ghost marks. The operation of a stripe hog is similar to the water blasting explained above. The drawbacks of a stripe hog are high water consumption (29 LPM or more), and higher initial cost.

Dry sandblasting: Dry sandblasting is an efficient method for removing line marking, but the downside is the dust it spreads into the atmosphere. Aggressive dry sandblasting may leave a confusing ghost mark or scar on the road and can roughen the blasted area.

Blackout method: Blackout method involves applying black or grey paint over the existing line marking to mask it.  However, many government authorities require that unwanted line markings must be removed and not blacked out as blacking out is purely a temporary measure. Blacking out can lead to confusion including:

  • On wet nights, blacked-out lines may be reflected by vehicle headlights and motorists traveling in the opposing direction may perceive the blacked-out lines as legitimate markings.
  • As the moving vehicles erode the blacked-out coating, they can change their color and gloss and create confusion in the minds of motorists, especially when sunlight reflects on them.
  • After some time the blacked-out area (black or grey paint) will wear out and reveal the original unwanted line markings.

Wet abrasive blasting: This process is also known as dustless blasting and vapor blasting, is one of the most environmentally friendly and protects the surface from undue wear and tear. This innovative technology has many benefits in line marking removal. It is discussed in detail in the following section.
Other less commonly used methods for line marking removal are burning the line marking, using chemicals to remove line marking, etc.
Since the majority of roads are regulated by government or regulatory authorities, it is worth noting their requirements for line marking paint removal. Below is an extract of the policy of the Northern Territory government department of transport on line marking removal.
When doing the line removal work, it must be ensured not to endanger the health, safety, or amenity of workers, road users, or the public in the area. For any operations carried out on the road, the safety of the workers and the public is the first priority. Removal of line marking should be carried out ensuring the following:

  • Minimize damage to pavement surfaces.
  • Noise pollution should be considered when finalizing a line removal method near built-up areas.
  • Grinding is permitted in certain circumstances, however, a combination of initial grinding followed by another removal process is required to achieve the final result. The grinding method is not recommended for line removal from sprayed seals or high-texture asphalt.
  • The line marking process should not leave behind any recognizable markings.
  • The removed marking and the material used for removing it should be contained, collected, and disposed of in an environmentally friendly manner.
  • There is no single method of line removal that works equally well on the wide variety of line marking materials available today, and often effective line removal can be achieved by using a combination of line removal methods.
  • Thermoplastic line marking materials require special considerations since the line marking is thicker than other paints.

IV. Wet abrasive blasting for line marking removal

The wet abrasive blasting or dustless blasting process involves mixing water and abrasive media inside a pressurized blast tank and combining it with compressed air to propel it onto the surface being blasted. The impact of the blast force makes light work of removing the paint without damaging the surface. This technique is similar to dry blasting but the additional element of water generates more impact and suppresses 95% of the dust.

V. Why is wet blasting a superior method for line marking removal?

Wet abrasive blasting offers the following advantages for line marking removal when compared to other processes:

  • Wet blasting is efficient and impactful as the water particles encapsulate the abrasive media and the saturated media creates a forceful impact removing the paint easily.
  • The use of water suppresses the dust and makes it safe for the environment, the operator, and the others in the area.
  • Dustless blasting removes the line marking with almost no traces left and it will not scarify and damage the underlying substrate.
  • Wet blasting works gently on the area that is line marked and provides a smooth feathered finish.
  • Wet blasting can be used with different abrasive media such as garnet, crushed glass, or soda bi-carbonate to suit each coating and each surface.
  • Wet blasting can remove all type of line marking paint including thermoplastic paint.
  • The amount of water used by a wet blast machine (less than 2 litres per minute) is much less than a water spraying machine (29 litres per minute or more) and is thus environmentally friendly.

Types of abrasive media used in the wet blasting process for line marking removal:

Wet blasting with soda bi-carbonate: Soda bi-carbonate is a single-use abrasive media with a Mohs hardness of 2.5. This property makes it extremely useful and effective for line removal on old asphalt surfaces also. A soft abrasive media like soda bi-carbonate uses minimum impact on asphalt road surface, gradually removes the line marking, and makes it looks like the surrounding asphalt. Working with soda bi-carbonate makes the process a bit slow, but the results will be very good. The line marking is removed without disturbing the underlying surface, and without scars or ghost marks. Soda bi-carbonate blasting may not be effective on thermoplastic or cold-applied plastic paint.

Wet blasting with garnet: Fine-grit garnet has a Mohs hardness of 7.5 to 8.5. It is good for line removal on concrete surfaces. Garnet is non-toxic, chemically inert, and a natural product. The blasting velocity needs to be adjusted and it is necessary to do a sample area before going for the complete work. Wet blasting with fine grit garnet and low blasting velocity may work on relatively hard asphalt also. This method can be used for all line markings.

Wet blasting with crushed glass: Fine-grit crushed glass has a Mohs hardness of 5 to 6, and maybe tried for line removal from concrete surfaces, since it is more economical than garnet. Recycled crushed glass is a waste byproduct making it environmentally friendly. It is capable of removing all types of line markings.

VI. Final word

Line markings play a crucial role in day-to-day operations. It is important to ensure that they are consistently maintained. One of the most suitable and environmentally friendly ways of line marking removal is through the use of a wet sandblasting machine.

The RapidBlastTM  is the only Australian made wet blasting machine and is manufactured and sold by Quantum Blast Australia. The Rapid BlastTM equipment is available in different sizes and can be tailored in different configurations and mounted on a purpose built trailer or a truck to be fully mobile at a fraction of the cost of other alternatives. It is a versatile piece of equipment with several applications and is very effective for line marking removal on all surfaces.

For more information on RapidBlastTM wet blast machine and mobile units please visit Quantum Blast at https://quantumblast.com.au/.

Phone:1300822569 E-Mail:sales@quantumblast.com.au

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Line Marking Removal

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